A. Human Pathogens

1. Flagellates
   1. Giardia
   2. Leishmania
   3. Trypanosoma (see below)
   4. Trichomonas
   5. Pfiesteria
2. Amoeboid
   1. Entamoeba
   2. Naegleria
3. Sporozoa (Spore Forming)
   1. Isospora
   2. Cryptosporidia
   3. Cyclospora
   4. Toxoplasma
   5. Eimeria
   6. Sarcocystis
   7. Plasmodia
   8. Babesia
4. Microspora (Spore Forming)
   1. Enterocytozoon
   2. Septata
   3. Nosema
   4. Pleistophora
   5. Encephalitozoon

B. Gastrointestinal Protozoa

1. Primarily in Immunocompromised Hosts
   1. Isospora
   2. Microspora
   3. Cyclospora
   4. Cryptosporidia
2. Any Host
   1. Giardia
   2. Entamoeba
   3. Balantidium
   4. Cryptosporidia (increasing)
   5. Cyclospora (increasing)
   6. Pfiesteria

C. Cryptosporidia [4,20]

1. Intracellular parasite
   1. 10 species of cryptosporidia
   2. C. parvum most common and is covered here
   3. C. felis, C. muris, C. meleagridis also found
2. Lifecycle
   1. Humans infected on ingesting oocytes
   2. The oocysts excyst and release infective sporozoites
   3. Sporozoites attach to apical membrane of host epithelial cell
   4. Enter cell and remain intracellular but extracytoplasmic (in a vacuole)
   5. Internalized sporozoite undergoes asexual reproduction, produces merozoites
   6. Merozoites infect other epithelial cells or mature into gametocytes
   7. Gametocytes are sexual form
3. Clinical Setting
   1. Fecal-oral transmission
   2. Most commonly symptomatic in immunocompromised (HIV) persons
   3. Also important in water-borne outbreaks, food contaminations
   4. Diarrhea, fever, abdominal cramps, vomiting, nausea, weight loss may occur
   5. Duration ~2 weeks in immunocompetent persons
   6. Jaundice, weight loss, and right upper quadrant pain in immunocompromised persons
   7. Also can infect animals
   8. Immunity primarily mediated by CD4+ T lymphocytes
4. Symptoms
   1. Strongly associated with watery diarrhea
   2. Nausea and vomiting can occur
   3. Usually self-limited in normal hosts
   4. Prolonged diarrhea with dehydration in immunodeficient patients (especially AIDS)
5. Diagnosis
   1. Must specifically request cryptosporidium evaluation
   2. Oocysts 4-6µm in stool specimens
   3. Infected intestinal epithelium seen as ~4µm blue dots on light microscopy
6. Treatment [26]
   1. Paromomycin (Humatin®): 25-35mg/kg po (3 divided doses per day)
   2. Nitozoxanide extremely effective, well tolerated
   3. Azithromycin (Zithromax®) has shown some activity
   4. Clarithromycin appears to protect against development of cryptosporidium in AIDS [8]
   5. Rifabutin is effective in prevention, with efficacy (>75%) similar to clarithromycin [8]
   6. Drug treatment is usually only instituted in HIV infection (or other immunosuppression)
   7. Anti-HIV retroviral therapy with a protease inhibitor improves clinical, histological, and microbiological responses as CD4 counts increase; organisms do remain dormant [7]
7. Nitazoxanide (Alinia®) [24,26]
   1. Nitrothiazolyl-salicylamide derivative
   2. Broad spectrum activity against protozoa, nematodes, cestodes, trematodes, bacteria
   3. Active against cryptosporiosis, particularly in HIV negative patients
   4. Three day course 100mg po bid cures ~50% of HIV negative patients
   5. Available as 100mg/5mL suspension
   6. Additional therapy cures ~90% of initial non-responders (HIV negative only)
   7. Dose age 12-47 months: 100mg q12 hours x 3 days
   8. Dose age 4-11 years: 200mg q 12 hours x 3 days

D. Isospora

1. Most commonly in AIDS patients in developing countries
2. Oocyst 20-30µm in stool specimens
3. Easily identified on small intestinal biopsy specimens as 20µm oval blue inclusions
4. Fecal-oral transmission; does not infect animals
5. Unboiled tap water is greatest risk factor [2]
6. Symptoms similar to those in cryptosporidia
7. Prolonged diarrhea in AIDS patients often with high morbidity
8. Treatment [17]
   1. Trimethoprim-sulfamethoxazole DS (TMP-SMX 160/800mg) bid po x 7 days
   2. Ciprofloxacin 500mg po bid x 7 days is >85% effective
   3. Both of these are also effective for cyclospora treatment
   4. Nitazoxanide (Alinia®) 100-200mg po qd x 3 days (as above) [26]
9. Prophylaxis
   1. Lifelong prevention is generally required unless immunosuppression is reversed
   2. Lower doses may be used for prophylaxis than for treatment

E. Cyclospora [5]

1. May cause diarrhea in normal as well as immunocompromised hosts
2. Mainly in overseas travellers, immunocompromised, contaminated food
3. Oocysts 8-10µm seen on set preparations of stool
4. Not seen on light microscopy of small bowel specimens (only electron1
   1. Similar to Isospora
   2. Contaminated food (raspberries) transmission most common [5,13]
   3. Incubation period about 1 week
   4. Protracted and relapsing gastroenteritis - typically 9-43 (mean ~21) days
5. Treatment [17]
   1. Trimethoprim-sulfamethoxazole DS (TMP-SMX 160/800mg) bid po x 7 days
   2. Ciprofloxacin 500mg po bid x 7 days is >85% effective
   3. Both of these are also effective for isospora treatment
6. Prophylaxis
   1. Lifelong prevention is generally required unless immunosuppression is reversed
   2. Lower doses may be used for prophylaxis than for treatment

F. Microsporidia

1. Three distinct species
   1. Enterocytozoon (Encephalitozoon) bieneusi
   2. Septata (Encephalitozoon) intestinalis
   3. Encephalitozoon hellum
2. Common cause of diarrhea in patients with AIDS in USA
3. Causes watery diarrhea with cramping; dehydration not uncommon
4. Spores are 1-2µm in stool specimens; difficult to identify
5. Small bowel specimens: 2-3µm enterocyte inclusions
6. Treatment
   1. Loperamide (Imodium AD®) or somatostatin reduce diarrhea
   2. Albendazole 400mg po bid is effective for Encephalitozoon infections
   3. Fumagillin 60mg qd x 14 days cured microsporidiosis in 12 of 12 patients tested [21]
   4. Clindamycin 300mg po qid for 1 year in a patient with AIDS was highly effective [10]
7. Effect of Anti-HIV Therapy [7]
   1. Combination antiretrovirals including a protease inhibitor
   2. Improves clinical, histological, and microbiological responses as CD4 counts increase
   3. organisms do remain dormant

G. Leishmania [14]

1. Obligate intracellular (macrophage) flagellated protozoan, related to trypanosomes
2. Worldwide ~20 million persons infected; ~400,000 new infections per year
   1. Epidemic of cutaneous leishmaniasis in Afganistan and Pakistan
   2. Epidemic of visceral infection in India and Sudan
   3. Occurs in other countries in Asia and Africa and Middel East
   4. In USA, mainly occurs in Texas
   5. Also occurs in South America and Central America
3. Major Species and Diagnosis
   1. L. tropica or mexicana - localized skin ulcer ("oriental sore") or diffuse cutaneous
   2. L. braziliensis - mucocutaneous lesions ("espundia")
   3. L. donovani - disseminated visceral disease ("kala-azar")
   4. L. major - endemic cause of leishmaneisis
   5. L. infantum and L. chagasi - visceral disease outiside of Indian subcontinent, Asia, Africa
   6. Diagnosis by direct visulatization of amastigotes in clinical specimens
   7. Spleen, bone marrow and lymph node material may be used
   8. DNA detection with polymerase chain reaction (PCR) is available
4. Types of Clinical Infection
   1. Subclinical infection
   2. Localized skin lesions
   3. Disseminated cutaneous lesions
   4. Mucosal lesions (disseminated)
   5. Visceral infection (kala-azar)
5. Therapeutic Overview
   1. Antimony - intralesional, parenteral; resistance in India and southern Europe
   2. Pentamidine - not very effective
   3. Amphotericin B - lipid formulations prefered with 5-10 day course, reduced side effects compared with standard amphotericin B (~98% effective for visceral disease) [28]
   4. Paromomycin - topical or parenteral; parenteral non-inferior to (~94% cure rate for visceral disease) and better tolerated than amphotericin B [28]
   5. Miltefosine - oral treatment given over 28 days; effective in antimony resistant disease
   6. Various antifungal azoles have been used
   7. Interferon gamma treats resistant Leishmanial disease well [3]
6. Localized Cutaneous Leishmaniasis (L. tropica or mexicana or major)
   1. Carried mainly by rodents (and dogs) and transmitted by infected sandflies
   2. Occurs in China, India, Asia, Africa, Mediterranean, Central America
   3. Pruritic papules appear on extremities or face ("oriental sore")
   4. Regional lymphadenopathy
   5. Papules ulcerate over months producing painless craters
   6. Spontaneous healing in 3-12 months
   7. Positive leishmanin skin test
   8. Antimonials, Amphotericin B (including lipid forms), and cycloguanil pamoate have activity
   9. Fluconazole (Diflucan®) 200mg po qd for 6 weeks causes healing of L. major cutaneous disease in 80% at 3 months compared with 34% on placebo [19]
7. Diffuse Cutaneous Leishmaniasis
   1. Unusual diseas of Ethiopia, Brazil, Dominican Republic, Venezuela
   2. Caused by varients of L. tropica or mexicana which do not stimulate cellular immunity
   3. Massive dissemination of initially localized skin lesions occurs
   4. Similar in appearance to lepromatous leprosy
   5. Negative leishmanin skin test
   6. Pentamidine and amphotericin B (including lipid formulations) have activity
   7. Oral miltefosine for 28 days is generally effective
   8. Somre reports of activity of oral ketoconazole
8. Mucocutaneous Leishmaniasis (L. braziliensis) [11]
   1. Carried by large forest rodents of tropical Latin America
   2. Transmitted by infected sandflies
   3. Primary skin lesion similar to oriental sore (above)
   4. Usually progressively enlarges to painful destructive lesions of mucocutaneous tissue
   5. Erosion of nasal septum, hard palate, or larynx can occur
   6. Systemic signs/symptoms of infection can occur
   7. Secondary bacterial infections are common
   8. Positive leishmanin skin test
   9. Treatment with antimonial agents or amphotericin B as for Kala-Azar
   10. Liposomal amphotericin B (AmBisome®) is also effective, better tolerated
   11. Vaccine with tubercule BCG + autoclaved leishmania reduced transmissions in boys [9]
9. Visceral Leishmaniasis (Kala Azar; L. donovani)
   1. Tropical and subtropical areas of every continent except Australia
   2. Disease is often acute and highly lethal
   3. Domestic dog is most common carrier; transmission is by sandflies
   4. Parasites disseminate in bloodstream and settle in reticuloendothelial organs
   5. Macrophages are infected most commonly; histiocytic proliferation follows infection
   6. Fever, hepatosplenomegaly, and cytopenias (bone marrow infection) occur
   7. Lymphadenopathy is also commonly found
   8. Negative leishmanin skin test; diagnosis by demonstration of organisms in biopsies
   9. Mortality in untreated disease is >75%
   10. Pentavalent antimonial drugs are efficacious in 35-65% of cases
   11. Kala azar in India very sensitive to lipid Amphotericin B 5-10 day course (90% cure)
   12. Oral miltefosine 50-100mg/day x 28 days is generally effective, well tolerated [12,15,25]
   13. Main side effects of miltefosine are vomiting (38%) and diarrhea (20%) [25]
   14. Resistant cases can be treated with pentamidine or amphotericin B (lipid complex) [6]
   15. Vaccine consisting of heat-killed L. major + BCG adjuvant is not effective for preventing visceral leishmaniasis [18]

H. African Trypanosomiasis (Sleeping Sickness) [22,23,27]

1. Caused by a Trypanosome Protozoan
   1. Sleeping Sickness is caused by T. brucei (several subspecias identified)
   2. Chagas' Disease is caused by T. cruzii (American trypanosomiasis)
2. Transmitted by bite of the Tsetse fly
   1. Chancre develops 2-3 days after bite of fly
   2. Parasitemia develops 2-3 weeks after bite
3. Clinical Disease
   1. Fever
   2. Tender lymphadenopathy
   3. Skin Rash
   4. Headache
   5. Altered Mental Status
   6. Mycoarditis and central nervous system (CNS) involvement may occur
   7. Heart failure and/or seizures (coma) may follow
4. Diagnosis
   1. Microscopic examination of lymph node aspirates or blood
   2. Lumbar puncture should be done as cerebrospinal fluid (CSF) may show organisms
   3. CSF may also be positive for Mott cells (morular cell) and positive agglutination
   4. Elevated levels of IgM specific for T. brucei may be used for screening
5. Treatment
   1. Positive CSF analysis indicates need for aggressive therapy or disease will be fatal
   2. Melarsoprol, a toxic arsenical which crosses blood-brain barrier, is used
   3. Melarsoprol 10 day course of 2.2mg/kg/d injections is as effective and easier to administer than the standard 26 day course [16]
   4. Suramin ± enflornithine (difluoromethylornithine) may be as effective and safer
   5. Enflornithine 100mg/kg to max 7gm IV q6 hours for 14 days very effective [23]
   6. In absence of CNS infection (Stage 1), suramin or pentamidine may be used
   7. Pentamidine 4mg/kg IM daily or alternate days for 7-10 doses
   8. Suramin is given as a test dose as 4-5mg/kg on Day 1, then initiate therapy 2 days later
   9. Suramin 20mg/kg (maximum 1gm) then on days 3,10,17,24,31; rapidly active
   10. Initial treatment followed by killing of organisms and systemic inflammation and edema

I. Pfiesteria

1. Dinoflagellate algea lives in ocean
   1. Can change into up to 22 distinct morphological forms
   2. Amoebic, cystic, and other
2. Thrives in high nutrient (nitrogen and phosphate) water
3. Found in coastal waters from Delaware Bay to Alabama Gulf Coast
4. Usually flourishes in areas of animal industrial waste disposal (animal feces pollution)
5. Toxin produced is lethal to fish and dangerous to humans
6. Produces "red tide"
7. Symptoms in Humans
   1. Exposure through fishing, swimming and other water sports
   2. Nausea and fatigue are prominant
   3. Migraines
   4. Skin lesions which do not heal
   5. Learning and memory problems (including dementia complex)
8. Diagnosis
   1. High suspicion
   2. Special cultures required
9. Treatment
   1. Cholestyramine has been used to treat patients exposed to Pfiesteria toxin
   2. Antibiotic agents specific for dinoflagellates have not been described

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